1. Field of the Invention
The field of the present invention is improvements in hydrostatic continuously variable transmissions comprising a pump cylinder in a hydraulic pump and a motor cylinder in a hydraulic motor, which cylinders are coaxially integrally coupled with each other to form a cylinder block, an annular inner oil passage and an annular outer oil passage which are formed in the cylinder block between a large number of cylinder bores provided in an annular arrangement in the pump cylinder and a large number of cylinder bores provided in an annular arrangement in the motor cylinder, so as to surround an axis of the cylinder block, a large number of first distributor valves disposed radiately in the cylinder block and adapted to be reciprocally moved radially of the cylinder block to put the large number of cylinder bores in the pump cylinder into alternate communication with the oil passages, a large number of second distributor valves disposed radiately in the cylinder block and adapted to be reciprocally moved radially of the cylinder block to put the large number of cylinder bores in the motor cylinder into alternate communication with the oil passages, a first eccentric ring engaged with the first distributor valves for providing the reciprocal movement to the first distributor valves in response to relative rotation between the cylinder block and an input member of the hydraulic pump, and a second eccentric ring engaged with the second distributor valves for providing the reciprocal movement to the second distributor valves in response to the rotation of the cylinder block, so that each cylinder bore in the pump cylinder is put into communication with the one inner oil passage in its discharge stroke and into communication with the other oil passage in its intake stroke, while each cylinder bore in the motor cylinder is put into communication with the one oil passage in its expansion stroke and into communication with the other oil passage in its contraction stroke, thereby providing the transmission of power between the hydraulic pump and the hydraulic motor through a hydraulic pressure.
2. Description of the Prior Art
Such a hydrostatic continuously variable transmission is already known, as disclosed, for example, in Japanese Patent Application Laid-open No. 20959/87.
In the continuously variable transmission disclosed in that publication, in order to freely changeover the hydraulic pump and the hydraulic motor between a power transmitting condition and a power interrupting condition, a large number of clutch valves are disposed radiately in axial arrangement with the first and second distributor valves for providing the opening and closing between the inner and outer passages by the radial movement thereof and adapted to be opened and closed by a third eccentric ring.
In such a transmission, however, there is a problem of a complication in structure, because the cylinder block and thus the transmission cannot be avoided from being increased in axial size and moreover, the three eccentric rings are required, from the fact that the three types of the first and second distributor valves and the clutch valves are axially disposed.